Check digits are used to ensure the accuracy of input data. A 7-digit code number has an extra digit on the right, called the check digit. The check digit is calculated as follows: • each digit in the number is multiplied by its digit position • the seven results are then added together • this total is divided by 11 • the remainder gives the check digit (if the remainder = 10, the check digit is X)

1. (a)(i)Calculate the check digit for the following code number. Show all your working. 4 2 4 1 5 0 8 ... Check digit[2]
2. (a)(ii)An operator has just keyed in the following code number: 3 2 4 0 0 5 X Has the operator correctly keyed in the code number? Give a reason for your answer.[3]
3. (b)(i)When data are transmitted from one device to another, a parity check is often carried out on each byte of data. The parity bit is often the leftmost bit in the byte. If a system uses even parity, give the parity bit for each of the following bytes: parity bit 1 1 0 0 1 1 0 parity bit 0 0 0 0 0 0 1[2]
4. (b)(ii)A parity check can often detect corruption of a byte. Describe a situation in which it cannot detect corruption of a byte.[1]

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